This invention relates to a device for measuring the angle of inclination of a workpiece surface and it is concerned in particular with measuring the flank angle of piston rings having a trapezoidal cross section. The device includes a feeler which is mounted on a holder and which can be positioned on the surface of the workpiece.
In an internal combustion engine, for example, it is a condition for the proper functioning of each piston ring that the latter, with its outer peripheral face, closely engages the cylinder wall and further, with a side face, closely engages the side wall of the associated piston groove. During operation of the engine, however, coked lubricating oil may often cause undesirable carbon deposits in the piston groove thus adversely affecting the radial mobility of the piston ring. By using piston rings of single-trapezoidal or dual-trapezoidal cross section in conjunction with similarly shaped piston groove cross sections, during radial ring motion there results an increase of the axial play between the piston ring and the piston groove, thus preventing a jamming of the piston ring in the groove. Further, such an arrangement effects a removal of oil carbon from the grooves. In order to achieve, however, a satisfactory flank seal between the piston ring and the piston groove, the flank angle (and its deviation from the permissible tolerances) has to be determined with precision.
In addition to maintaining the trapezoid angle within the desired values, the oblique position of the cross section of the piston ring is also of significance for ensuring a proper operation. The trapezoid angle is defined as the angle formed by the two opposite ring flanks of the sum of the two flank angles, particularly in piston rings having a dual-trapezoidal cross section. The oblique position of the cross section of the piston ring is defined as the deviation of the lower, planar ring flank of a single-trapezoidal ring or the deviation of the angle-halving line of the trapezoid angle of a dual-trapezoidal piston ring from a radial plane oriented perpendicularly to the piston ring axis. By single-trapezoidal piston rings or piston rings having a single-trapezoidal cross section there are meant piston rings whose cross section is a trapezoid in which one of the non-parallel sides is perpendicular to the piston ring axis. By dual-trapezoidal piston rings or piston rings having a dual-trapezoidal cross section, there are meant piston rings whose cross section is a trapezoid in which both non-parallel sides are oriented obliquely with respect to the piston ring axis. Thus, a dual-trapezoidal piston ring could be regarded as two back-to-back arranged single-trapezoidal piston rings.
For measuring the ring height of a single-trapezoidal or dual-trapezoidal piston ring, a device is known which is disclosed in German Offenlegungsschrift (Laid-Open Application) No. 1,902,470 and in which there are provided two axially oppositely located piston ring holders which engage the ring flanks and one of which is connected with a settable measuring device. The piston ring holders are rotatably supported in prismatic guides for adapting them to the flank faces having different flank angles. The holders which adapt themselves to the particular flank angle in each measuring process serve solely for the symmetrical alignment of the piston ring.
In the technical publication K8 entitled "Neue Verfahren zur Bestimmung der Qualitat von Kolbenringen" (New Methods of Determining the Quality of Piston Rings) and issued by the firm Friedrich Goetze AG in Burscheid, Federal Republic of Germany, there is further described a device for measuring the flank angle of piston rings. The device described therein has two feelers arranged to a predetermined radial distance from one another and constituting a first feeler pair. Further, relative to a line of symmetry of the cross section of the piston ring in case of dual-trapezoidal piston rings, there is provided a second feeler pair arranged opposite the first feeler pair. The feelers are connected with inductive path sensors known by themselves, so that the individual measured values may be read by means of a preferably electric display device. The accuracy of the trapezoid angle which is computable based on the measured values depends on the accuracy of the radial distance between the two feelers.